Safes, fire-proof file cabinets, and various fire resistant boxes and cabinets have consistently avoided use of materials that are flammable or unable to survive the high temperatures used in current fire-resistance tests. They have been made with external and internal steel shells filled with an insulating material so that the entire construction is formed of nonflammable materials. The external steel shell gives structural strength and protection and cooperates with the internal steel shell to support the insulation material and form a strong box or cabinet. Present insulation materials for fire-proof safes and cabinets are often moldable materials, and various mixes of concrete and other materials that contain a substantial volume of chemically bonded and free excess water are preferred. The construction of such safes and cabinets involves shaping and fitting together the parts of the steel shells, molding the insulation in place, and cleaning and finishing operations.